1. Field of the Invention
The present invention relates to a recording sheet and an image recording method using the recording sheet. Particularly, the invention relates to a recording sheet having a surface that is not subjected to special coating, or so-called plain paper, and an image recording method for ink jet recording and electrophotographic recording using the recording sheet.
2. Description of the Related Art
The ink jet recording method is characterized in that color printing is easy, energy consumption is low, a low level of noise is generated during recording, and printers therefor are manufactured with low costs. Ink jet recording devices have been widely used in offices in recent years due to such advantages, and are often used together with electrophotographic apparatus such as a laser printer and copiers.
Recording media (recording sheets) such as so-called plain paper, a colorless film and a transparent film are used for the ink jet recording method. In particular, the plain paper is most frequently used when the ink jet recording device is used in the office together with a laser printer or copier, since images are readily formed on the plain paper using these electrophotographic recording machines, and since the plain paper is inexpensive and readily available. Accordingly, it is quite important to improve printability of the ink jet recording method on the plain paper. However, there have been the following problems in printing on the plain paper by conventional ink jet recording methods.
(1) A so-called feathering phenomenon occurs by efflux of the ink along the fiber of paper. Image quality of letters, particularly of special letters, is largely impaired by this feathering phenomenon.
(2) The surface of the so-called plain paper is usually sized (made to be water repellent). Consequently, adsorption of the ink is retarded, and so-called inter color bleeding (ICB) occurs at the portions where different colors contact one another.
(3) Portions in contact with printed surfaces become stained when printed documents are piled since absorption of the ink is retarded due to sizing (water repellent treatment) applied on the surface of the paper.
(4) Colorants in the ink tend not to stay on the surface of the plain paper, whereby coloring is insufficient.
(5) Printed images can be seen from the back surface (from the surface opposed to the printed surface) through the paper since the colorants in the ink permeate into the paper to make printing on both surfaces impossible.
While the ink jet printer is desired to have a high printing speed comparable to that of the laser printer for extending the use of the ink jet printer into office uses, it has been quite difficult to establish compatibility among ink absorption (dryability), improved image quality and applicability to two-sided printing.
In a method proposed for solving these problems, coagulation and precipitation of ink components are accelerated using a recording sheet whose surface is treated with cationic substances such as cationic polymers and multivalent metal salts for improving image quality. However, the effect of accelerating coagulation and precipitation is weakened, and in particular feathering becomes evident, when a rapidly permeating ink such as that used for high speed printing is used. Since surface treatment with ionic substances results in a decrease in electrical resistance of the sheet due to an excessive reaction to environmental changes, transfer of toners in a laser printer or copier using the electrophotographic method may be adversely affected (see, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 10-166713, 7-257017, 8-216498 and 10-100531).